1. FIELD OF THE INVRENTION
This invention relates generally to an industrial robot and, more particularly, to a multi-function industrial robot that performs a plurality of different operations, using different, selected tools.
2. DESCRIPTION OF THE BACKGROUND
Industrial robots are now known for use in various industries because of accuracy of repetition and high efficiency, and many such robots are employed on assembly lines, in which the robots are required to perform numerous different sequential operations, such as positioning workpieces in a working position, tightening bolts or screws, welding, and the like. In order to be able to perform these different operations, the robots must be equipped with several different tools at their working ends. Therefore, when a single robot is used to perform various operations, it is necessary to change tools according to the required operations and predetermined schedule of operations.
There are typically two known ways to change tools to enable multi-operations using a single robot, one of which is to stock all necessary tools in a tool stocker, with the tools specifically arranged in the tool stocker so that the robot can pick up the necessary tools according to the programmed schedule of operations. In this technique, the robot is programmed to move its working end to a point opposite the tool stocker at the conclusion of every operation, in order to change tools. This involves a waste of time and energy in repeatedly moving the working end of the robot between the tool stocker and the working position, which clearly lowers the robot's efficiency. Moreover, this drop in the robot efficiency becomes more significant as the number of operations increases.
To avoid these extra motions of the robot's working end, it is known to provide a turret for mounting necessary tools. The turret is actuated by a turret controlling servo that positions the tool intended to perform the next operation opposite the work position, which eliminates the extra movements of the working end between the working position and the tool stocker. Nevertheless, this system requires a turret controlling servo apparatus that generally involves at least a servo motor and a reduction gear assembly and, because of the additional weight of the turret caused by the tools and the turret controlling servo, the moment of inertia of the robot arm is increased significantly. This increased inertia limits the top speed of the working end in order to provide sufficient accuracy in positioning the working end at the working position. Furthermore, even at a limited arm speed, back-lash inherent in the reduction gear assembly lowers the accuracy in positioning of the working end.